Taurine depletion in very low birth weight infants receiving prolonged total parenteral nutrition: role of renal immaturity

In a prospective, controlled study, plasma and urinary taurine concentrations were determined weekly, between postnatal weeks 3 and 18, in (1) seven sick infants (gestational age less than 28 weeks, birth weight less than or equal to 1000 gm) who received a taurine-free total parenteral nutrition solution for 32 to 49 days (group P) and who subsequently were formula fed and (2) eight sick infants matched by gestational age and birth weight, who received formula or human milk from day 3 to 4 of life (group E). Ten healthy full-term infants ranging in age from 1 to 18 weeks and fed with formula provided normal values (group C). Significantly lower mean plasma taurine values (range 1.59 to 3.43 mumol/dl) were found between postnatal weeks 3 and 7 in group P compared with group E (range 5.54 to 6.97 mumol/dl) and with group C (5.6 +/- 0.34 mumol/dl). After initiation of feeding, plasma taurine concentrations in group P increased to normal. Markedly elevated values of mean fractional excretion of taurine, 38% to 56%, were found between weeks 3 and 5 in group P and E compared with group C (15.5 +/- 3.2%). In contrast, during the same period, low urinary taurine values (4.9% to 6.7%) were found in two larger, older infants receiving total parenteral nutrition whose plasma taurine values were in the normal range. After week 5, urinary taurine values were in the control range in all groups. We conclude that the absence of taurine in total parenteral nutrition solutions administered to very low birth weight infants and the limited ability of the immature kidney to adapt to low taurine intake by "up-regulation" of tubular taurine reabsorption may result in depleted taurine body pools during the first weeks of life. This inability to conserve taurine by the immature nephron could potentially have a deleterious effect on the developing brain and retina in these infants, and indicates a possible need for taurine supplementation.     

Intrauterine growth of infants with chorioamnionitis

The relationship between chorioamnionitis and fetal growth was examined by analysing the data of 299 infants with chorioamnionitis and the data of 296 infants with normal placentas. Six parameters were used for estimation of fetal growth: birth weight, length, head circumference, ponderal index, the ratio of length to head circumference and gestational age. Chorioamnionitis was identified, when at least 10 neutrophils per microscopic high-power field were present in the plate of placenta. There was no significant difference between the two groups at full term infants. The comparison could not be made under 37 weeks of gestation. It was concluded that chorioamnionitis probably did not impair particularly the fetal growth.     

Taurine in developing brain, liver and muscle in infants

In order to evaluate tissue taurine storage during pregnancy, we determined the taurine concentration of a skeletal muscle (abdominal wall), the brain (left parietal lobe), and the liver (right lobe) in 41 children aged 1-10 days, born after 24-41 weeks gestation. Samples were obtained during autopsy. Taurine dosage was carried out by gas chromatography. Muscle and liver taurine concentrations decreased with the duration of gestation. For a given duration of pregnancy, there was no correlation between birth weight and these three tissue concentrations. From these results, we estimate that the fetus accumulates 35-40 mumol/24 h of taurine during the last 3 months of gestation.     

Relationship of serum bilirubin levels to ototoxicity and deafness in high-risk low-birth-weight infants

During a 4-year period, 12 premature infants, all less than 34 weeks of gestation and all with a bilirubin level above 240 mumol/L (14 mg/dL) were determined to have bilateral sensorineural deafness. In order to to investigate how far the hyperbilirubinemia or any a associated factor might have been a causative factor, all infants of 34 weeks of gestation or less who had a serum bilirubin level above 240 mumol/L were investigated. For a period of 4 years, 99 infants meeting these criteria were classified as high risk or low risk on the basis of perinatal risk factors. Eight of the 22 high-risk infants with birth weight less than 1,500 g, but only two of 43 high-risk infants with birth weight greater than 1,500 g were deaf (P less than .05). The deaf infants were also matched with infants of normal hearing who had similar bilirubin levels and the same number of adverse perinatal factors. The mean duration of hyperbilirubinemia was significantly longer in the deaf infants (P less than .02), and they appeared to have a greater number of acidotic episodes while they were hyperbilirubinemic. These findings suggest that in healthy preterm infants with birth weight greater than 1,500 g, high bilirubin levels carry little risk, whereas a serum bilirubin level greater than 240 mumol/L in high-risk preterm infants with birth weight of 1,500 g or less is associated with a high risk of deafness.     

Birth weight patterns in rural undernourished pregnant women

OBJECTIVE: To study the birth weight pattern in chronic as well as currently undernourished pregnant women. DESIGN: Prospective study of rural pregnant women by following eligible women. SETTING: Two adjoining blocks of rural Varanasi. METHOD: 3700 pregnant women from rural areas of Varanasi for whom data for anthropometry, hemoglobin, dietary intake, birth weight, fundal height and abdominal girth at 16 +/- 2, 28 +/- 2 and 36 +/- 2 weeks of gestation were recorded. Outcome measure was birth weight pattern of newborns. RESULTS: Of the births, 7.2% were < 2250 g and 27.4% < 2500 g. The weekly birth weight increments in gestation 36-42 weeks were 5-53 g, only. The fundal height did not increase during 35-39 weeks of gestation (lower by 5 cm as compared to normal). Nutrition supplement in the third trimester significantly increased fundal height and abdominal girth. Fundal height below 24.5 cm at 28 weeks of gestation (1368 women) was associated with higher low birth weight deliveries. CONCLUSION: Birth weight and fundal height increments during later pregnancy are low in undernourished pregnant women. Fundal height < 24.5 cm at 28 weeks of gestation identified women with higher risk for lowbirth weight infants. The prevalence of low birth weight was 27.4% and of prematurity was 6.6%.     

Hypothalamic-pituitary-adrenal axis function in very low birth weight infants treated with dexamethasone

The effect of dexamethasone therapy on hypothalamic-pituitary-adrenal axis function was prospectively investigated in very low birth weight infants with bronchopulmonary dysplasia. Ten infants (mean +/- SD birth weight 825 +/- 265 g, gestation 25.8 +/- 1.9 weeks, postnatal age 33.1 +/- 17.7 days) initially received intravenous dexamethasone, 0.5 mg/kg per day for 3 days, and then were weaned over a period of 45 +/- 19.0 days to a replacement dose, followed by a metyrapone test. Morning plasma cortisol and 11-deoxycortisol levels were measured before and after an oral metyrapone dose given at midnight. Five infants (group A: birth weight 876 +/- 313 g, gestation 26.2 +/- 1.3 weeks, age of entry 31.8 +/- 22.8 days) had normal metyrapone test results, and five infants (group B: 778 +/- 234 g, 25.4 +/- 2.5 weeks, 34.4 +/- 13.4 days) had suppressed test results. Group A infants, in comparison with group B infants, had higher basal cortisol plasma levels (14.52 +/- 12.53 and 3.00 +/- 1.38 micrograms/dL, P = .047), higher postmetyrapone 11-deoxycortisol plasma levels (3.11 +/- 3.93 and 0.55 +/- 0.51 micrograms/dL, P = .028), larger differences between basal and postmetyrapone cortisol levels (7.10 +/- 4.67 and 2.12 +/- 1.31 micrograms/dL, P = .047), and larger differences between basal and postmetyrapone 11-deoxycortisol levels (2.99 +/- 3.93 and 0.29 +/- 0.25 micrograms/dL, P = .009). The hypothalamic-pituitary-adrenal axis function in group B infants eventually returned to normal when they continued to receive low-dose dexamethasone therapy after a period of 36.8 +/- 16.6 days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Taurine requirement of premature infants in parenteral nutrition]

The aim of our studies was to clarify, which dose of taurine should be added to amino acid solutions, in order to achieve plasma levels in premature infants as they are found during nutrition with mother's milk. In 22 premature infants born in the 30th-35th week of gestation plasma taurine levels during parenteral nutrition were measured on the 5th-9th day of life before and after infusing an amino acid solution supplemented with taurine. For analysis the principle of chromatographical ion exchange was applied. The requirement of taurine was calculated by means of a linear regression between supply and blood level. The mean plasma taurine levels before substitution were 88.7 mumol (95%-range of tolerance: 32.8-240 mumol/l). In premature infants with cerebral haemorrhages significantly higher plasma taurine levels were observed. Continuous parenteral taurine supply of approximately 0.05 g/kg/day was able to raise the taurine level by about 70 mumol/l, which caused a plasma taurine level of above 100 mumol/l in any case. During parenteral nutrition it is possible to achieve taurine levels as high as in breastfed neonates by substituting taurine at an amount of 0.05 g taurine per kg body weight.     

Placental alcohol metabolism in chronic alcohol abuse

The activities of aldehyde dehydrogenase (ALDH; EC 1.2.1.3) and alcohol dehydrogenase (ADH; EC 1.1.1.1) were measured in term placentas of 13 alcoholic women and 16 matched controls. With acetaldehyde 8 mmol/l as substrate, the ALDH activity was 29.1 +/- 12.2 and 34.4 +/- 15.3 mU/g of wet weight (mean +/- SD; p greater than 0.4) for alcoholics and controls, respectively. With 50 mumol of acetaldehyde, ALDH activity was undetectable in both groups. No ADH activity could be detected in the placentas. The weights of placentas and newborns were significantly lower in the alcoholic group (placentas: 526 +/- 116 vs. 653 +/- 77 g, p less than 0.005; newborns 2,878 +/- 417 vs. 3,595 +/- 346 g, p less than 0.001). The results suggest that in chronic alcohol abuse, the placenta plays a negligible role in the metabolism of ethanol and acetaldehyde.     

Intestinal absorption of vitamin E in low birth weight infants

Intestinal absorption of dl-alpha-tocopheryl acetate was studied in low birth weight infants. Vitamin E was given from the first day of life, either as a water-soluble (Ephynal) or as a lipid-soluble preparation (E-vitamin). Serum-alpha-tocopherol concentrations were determined before treatment and on days three and seven. Treatment with both vitamin E preparations increased serum-alpha-tocopherol on day three and seven. The mean serum-alpha-tocopherol +/- SD on day seven were 41.4 +/- 10.7 mumol/l for the Ephynal group and 26.7 +/- 12.5 mumol/l for the E-vitamin group, this difference being statistically significant (p less than 0.025). Oral feeding seems to influence the absorption of tocopherol from E-vitamin, as the infants with the highest serum-alpha-tocopherol concentrations were those with the highest oral/total feeding ratios. In infants with birth weight less than 1 000 g treatment with 25 mg Ephynal/day was found to increase serum-alpha-tocopherol on day seven to 46.9 +/- 12.3 mumol/l (mean +/- SD). This concentration is comparable to those reported by others using higher doses of oral vitamin E.     

Clearance of calcium across in situ perfused placentas of intrauterine growth-retarded rat fetuses

Maternofetal clearance of 45Ca and 51Cr-EDTA (diffusional marker) were simultaneously measured across in situ perfused placentas of intrauterine growth-retarded (IUGR) and control rat fetuses on d 20 of gestation. IUGR was induced by uterine artery and vein ligation on d 17 of gestation. Control fetuses and their placentas were taken from sham-operated dams. We hypothesized that calcium transfer would be impaired across placentas of IUGR fetuses. The mean body wt of IUGR fetuses was 42% lower, and the mean nose-anus length was 16% lower than those of control fetuses. The mean total calcium content of IUGR fetuses was significantly lower than that of control fetuses, but not when it was normalized to body wt. The mean maternal whole blood ionized calcium concentration was not significantly different in the two groups. The materno-fetal clearance of 45Ca across IUGR placentas was significantly lower than that across control placentas (IUGR = 35.2 +/- 1.9 micro L/min/g placenta, mean +/- SEM; control = 93.1 +/- 12 microliters/min/g placenta, p less than 0.002). In contrast, the maternofetal clearance of 51Cr-EDTA, the reference diffusional marker, was not significantly different across IUGR and control placentas. We conclude that maternofetal transfer of calcium is reduced across placentas of IUGR rat fetuses.     

Inorganic sulfate metabolism in the very low birthweight infant

The effect of vitamin D supplementation on inorganic sulfate metabolism was examined in very low birth weight (less than 1,500 g) infants at biweekly intervals after birth until 6 weeks of postnatal age. Baseline serum sulfate concentrations were significantly higher in all infants (471 +/- 24 mumol/l, n = 80) than in adults (299 +/- 25 mumol/l, n = 17). In controls, the levels did not change significantly over the ensuing 6 weeks, although serum creatinine declined. Urinary sulfate excretion rose significantly to near adult levels by 2 weeks. Both urine and serum sulfate were correlated with weight gain but not with estimated glomerular filtration rate, suggesting that factors other than renal clearance have a preponderant influence on serum sulfate in these infants. At 6 weeks, the mean serum sulfate in the high-dose group (receiving 2,170 +/- 23 U/day of vitamin D, n = 41) was significantly higher than in controls (receiving 360 +/- 22 U/day, n = 40). In all infants, there was a significant correlation (r = 0.36, p less than 0.001) between serum sulfate and 25(OH)-vitamin D concentrations, but not other analytes or clinical variables, suggesting that vitamin D may be one of the factors modulating sulfate metabolism in the newborn period.     

Trace elements in meconium from preterm and full-term infants

Meconium samples from 23 preterm infants (birth weight = 1,097 +/- 359 g; gestational age 29 +/- 3 weeks, mean +/- SD) and 27 full-term infants (3,453 +/- 476 g; 39.5 +/- 1 weeks) were analyzed for zinc, copper, manganese, chromium and iron by atomic absorption spectrometry. Compared to meconium from preterm infants, full-term infants had an elevated (p less than 0.05) total excretion (microgram) of zinc (957 +/- 545 vs. 503 +/- 506), copper (245 +/- 256 vs. 128 +/- 94) and manganese (62 +/- 55 vs. 29 +/- 29), but not iron (190 +/- 147 vs. 332 +/- 532) or chromium (0.4 +/- 0.19 vs. 0.75 +/- 1.0). Two preterm infants had high losses (1.5 and 2 mg) of iron in their meconium. Zinc, copper and manganese losses into meconium appear to increase with gestation, whereas iron and chromium losses occur early in gestation and may be reabsorbed by term.     

Relation between maternal body composition and birth weight

In order to establish the relationship between maternal body composition indicators (fat-free mass, fat mass, total body water) and birth weight, a cross-sectional study was designed, based on 196 pairs of mothers and live singleton newborns with gestational age of 37 weeks or more. Immediately after delivery, the mothers were interviewed to obtain information about different birth weight predictors. An analysis of maternal body composition through bioelectric impedance was held. Multiple linear regression was used to measure the effect of each variable on birth weight. The birth weight mean was 3,251 +/- 514 g. Maternal height was 160.44 +/- 6.3 cm, total net weight gain was 5.85 +/- 5.15 kg, fat mass consisted of 15.84 +/- 6.72 kg, and fat-free mass was 50.42 +/- 7.65 kg; total body water was 34.82 +/- 5.61 liters. The model which included total body water and all predictors found to be associated with birth weight in the bivariate analysis (maternal age, gestational age, gender, placenta weight, and placenta weight squared) was found to be the best in explaining the variability of birth weight (R(2) = 45.26%). Fat mass was an important predictor only in the subgroup of women within the low tertile of body mass index. In conclusion, fat-free mass and total body water explained a major proportion of the variability of birth weight in comparison with the mother's weight gain during the pregnancy period, which has already been considered an important predictor of birth weight.     

Dietary zinc intake and growth during infancy

Energy, protein, zinc intake, and weight and length were monitored at 3, 6, and 12 months in 50 preterm infants (corrected for gestational age) (mean birthweight, 1,054 +/- 234 g; mean gestation, 29 +/- 2.5 weeks) and 60 full-term infants (mean birthweight, 3,509 +/- 269 g; mean gestation, 40 +/- 1 weeks). Mean energy and protein intake (per kilogram body weight) was higher (p less than 0.05) for the preterm infants at all times and met the recommended levels for preterm infants. No significant differences in zinc intake (per kilogram body weight) between the two groups existed, and at 3 months, mean zinc intake in the preterm group (per kilogram body weight) was below the recommended level for full-term infants. At no time were the growth percentiles of the preterm group equal to those of the full-term group. Multiple regression equations predicting length at 3 months and weight at 12 months for all the infants were significant, the significant variables being length at birth and zinc intake (milligrams per day) at 3 months, and weight at birth and dietary zinc intake (milligrams per day) at 12 months, respectively. Results indicate that zinc intake played a more important role in explaining the length at 3 months and weight at 12 months than did any other variables, including intakes of protein and energy, gestational age, socioeconomic index of the father, midparent height, sex, and age of introduction of solid foods. Results thus support the suggestion that infants, especially those born prematurely, are at risk for inadequate intake of dietary zinc.     

Rate of intrauterine growth retardation at the Leipzig Perinatal Center comparing the years 1982 to 1984 with 1987 to 1989]

Referring to the number of all live-born children, hypotrophic newborn (IUGR) were classified at the Centre for Perinatal Care in Leipzig into two periods of time. Based on the 5th Kyank-percentile 6.5% hypotrophic newborn were classified into period A (1982-1984) and 5.0% hypotrophic newborn were classified in period B (1987-1989). The proportion of hypotrophic newborn with a birth weight < 2500 g amounted to one quarter of all infants (except multiple birth) with low birth weight in period A and to one fifth (20.7%) in period B. The decrease in the rate of hypotrophy in these infants affected nearly exclusively the mature ones. The number of infants with extreme intra-uterine growth retardation amounted to 29% (99 in 329) in period A and to 24% (58 in 238) in period B. The rate of hypotrophy in stillbirths decreased from 44% to 33%. In this process the proportion of extremely hypotrophic stillbirths amounted to 47% in period A, whereas it decreased to only 26% in period B.     

Analysis of the efficacy of urine culture as part of sepsis evaluation in the premature infant

BACKGROUND: Premature infants have a higher incidence of urinary tract infection (UTI) than full term infants. UTI in premature infants can present with signs of sepsis: poor weight gain; temperature instability; metabolic acidosis; poor feeding; and abdominal distention. OBJECTIVE: The purpose of this study was to determine the usefulness of routine urine culture as part of a sepsis evaluation in the preterm infants. METHODS: We conducted a retrospective review of all infants with birth weight <1500 g (very low birth weight) who underwent sepsis evaluation at MetroHealth Medical Center between January 1991 and February 1998. All infants from whom urine and blood specimens were collected concomitantly for culture as part of a sepsis evaluation were included. RESULTS: Included were 538 infants. Their mean gestational age was 28.5 +/- 2.7 weeks, and mean birth weight was 1072 +/- 276 g. Blood and urine specimens for culture were taken from 349 infants on admission or in the first 24 h of life (Group A), their mean birth weight was 1147 +/- 244 g, and mean gestational age was 28.9 +/- 2.6 weeks. None of these infants had positive urine cultures; 8 infants (2%) had positive blood cultures. Blood and urine specimens were obtained from 189 infants later between Days 6 and 150 of life (Group B); their mean birth weight was 933 +/- 278 g, and mean gestational age was 27.5 +/- 2.5 weeks. Forty-eight infants (25.3%) in Group B had positive urine cultures, and 79 infants (41.7%) had positive blood cultures. Eighteen infants (38%) with positive urine cultures had positive blood cultures, and 30 infants (62%) had negative blood cultures. CONCLUSIONS: There is minimal benefit in obtaining urine cultures from very low birth weight infants as part of a sepsis evaluation in the first 24 h of life. It is important to obtain urine cultures from older infants with signs of sepsis to identify patients with UTI with or without bacteremia.     

Supplementation with human milk protein improves growth of small premature infants fed human milk

We investigated the influence of human milk protein and medium-chain triglyceride supplementations of human milk feedings on the growth of very low birth weight infants during their first weeks of life. A group of 44 preterm infants with birth weights of less than 1,520 g and a mean gestational age of 30.3 weeks was randomly divided into four groups to receive plain human milk or human milk supplemented with human milk protein (0.9 g/dL), with medium-chain triglycerides (1 g/dL), or with both. The medium-chain triglyceride oil supplementation did not influence the growth of these infants. The infants given supplementary protein gained weight faster during weeks 4 to 6 than those without (18.5 +/- 0.7 v 15.1 +/- 0.6 g/kg/d; mean +/- SEM; P = .001). After 4 weeks of age the infants given supplementary protein had a mean weight gain equal to the mean intrauterine rate, in contrast to the infants of the other groups, who grew more slowly until age 6 weeks. Furthermore, we found a correlation between serum albumin concentration and weight gain during the seventh week of life (P = .018). The length growth velocity for the infants with protein supplementation was 0.99 +/- 0.06 cm/wk (mean +/- SEM) and for those without 0.83 +/- 0.05 cm/wk (P = .043). There was no difference in growth of head circumference between the groups. We conclude that human milk protein supplementation improves the growth of small premature infants fed human milk, and that the protein concentration of bank milk is insufficient for their adequate growth.     

Procalcitonin in preterm infants during the first few days of life: introducing an age related nomogram

OBJECTIVE: To determine normal concentrations of procalcitonin in preterm infants shortly after birth and to assess its accuracy in detecting bacterial infection. METHODS: Blood samples of 100 preterm infants were prospectively drawn during the first 4 days of life for determination of procalcitonin concentration. Infants were classified into four groups according to their sepsis status. RESULTS: Mean (SD) gestational age and birth weight were 32 (2.9) weeks and 1682 (500) g respectively. A total of 283 procalcitonin concentrations from healthy infants were plotted to construct nomograms of physiologically raised procalcitonin concentration after birth, stratified by two groups to 24-30 and 31-36 weeks gestation. The peak 95th centile procalcitonin concentration was plotted at 28 hours of age; values return to normal after 4 days of life. Only 12 infants were infected, and 13 of their 16 procalcitonin concentrations after birth were higher than the 95th centile, whereas samples taken at birth were lower. In a multivariable analysis, gestational age, premature rupture of membrane, and sepsis status influenced procalcitonin concentration independently, but maternal infection status did not. CONCLUSIONS: The suggested neonatal nomograms of preterm infants are different from those of term infants. Procalcitonin concentrations exceeding the 95th centile may be helpful in detecting congenital infection, but not at birth.     

Hyperammonemia in hypoglycemic preterm neonates

Plasma glucose, blood urea nitrogen, and ammonia were measured simultaneously in 44 newborns a few hours after birth. When the concentration of plasma glucose was below 30 mg/dl, plasma ammonia concentration was significantly higher (129 +/- 67 mumol/l) than in normoglycemic infants (74 +/- 33 mumol/l; p less than 0.01). Blood urea nitrogen was slightly lower in hypoglycemic infants (3.65 +/- 0.7 mmol/l) than in the control group (4.5 +/- 1 mmol/l) but the difference was not significant. These data show that hyperammonemia can be associated to hypoglycemia in low birth weight infants. Therefore, further investigations are required to determine the link between urea and glucose production rates in hypoglycemic newborns and whether hyperammonemia participates in the deleterious effects of hypoglycemia on the neonatal brain.     

早产儿视网膜血管发育成熟度的研究

目的 研究早产儿出生时视网膜血管的发育及其影响因素,与早产儿视网膜病(ROP)发生之间的关系.方法 2006年10至12月,在北京军区总医院新生儿监护病区住院的不同胎龄和出生体重的84例新生儿,于生后1周内,扩瞳后用Retcam Ⅱ数码照相机拍摄眼底照片,评价视网膜血管化的程度,分析母亲和婴儿因素对视网膜血管化的影响.并追踪观察视网膜血管化程度与ROP发生的关系.计数资料用四格表X2检验,计量资料以x±s表示,两样本均数行t检验.结果在本组84例中,视网膜血管化达到Ⅰ区和Ⅱ区在胎龄<30周早产儿组中为91.7%(11/12),在胎龄31～33周组为46.2%(12/26),在胎龄34～36周组为3.84%(1/26),在胎龄37～40周组为0(0/20);在出生体重<1500 g组为80%(12/15),1500 g<出生体重<1700 g组为57.1%(8/14),1700 g<出生体重<2000 g组为36.4%(4/11),在2000 g组为0(0/44).单变量分析显示胎龄(F=31.9193,P=0.000)、出生体重(F=32.4532,P=0.000)、产前使用糖皮质激素(F=36.9391,P=0.000)、表面活性物质(F=24.000,P=0.0000)、母亲营养状态(F=4.184,P=0.041)、RDS(F=17.6191,P=0.000)、生产方式(F=10.972,P=0.0022)和需氧超过48 h(F=22.076,P=0.0000)等和视网膜的不成熟有关.多变量分析显示视网膜血管化主要受胎龄(95%CI=1.57～261.728,P=0.021)影响.追踪观察视网膜不成熟的24例早产儿,最终发现有15例发生ROP,占62.5%(X2=45.1087,P=0.000).结论在胎龄31～34周的早产儿视网膜血管化存在较大的变异性.母亲和胎儿因素可能影响出生时视网膜的血管范围.胎龄是影响视网膜成熟度的主要因素.不成熟的视网膜是发生ROP的根本原因.